There is a famous hadith that Muslim Ummah will split into seventy-three directions, and they will all be in Hell , except one, it is Ahlu-Sunnah Wal Jama'a.

Al-Sakhawi says in "al-Maqasid al-Hassan": "Hadith of the "division of the community" narrated by Abu Dawud and al-Tirmidhi, who said: "The hadith hasan saheeh". Also Abu Dawud narrates this hadeeth from Abu Hurayrah, may Allah be pleased with them: "The Jews were divided into 71 or 72 sects as were the Christians. And my community is divided into seventy-three course, and all of them in the Fire except one. We asked: "Who are they, O Messenger of Allah?" He replied: "Who (is of the same), then (Practicing) I and my companions". Also Ibn Hibban and al-Hakim gave this hadith in his "Sahih". Al-Hakim said, "This is the greatest hadith in questions of foundations of (religion)"".

Tirmidhi, Ibn Hibban, al-Hakim, al-Dhahabi, al-Munzari, Al-Shatybi spoke about the reliability of this hadith in "Al-itisam" and al-Suyut in "Al-Jami al-Sogir".

With regard to the statements of some modern "thinkers" of the unreliability of this hadith or part of it "and all of them in the Fire except one", their criticism of hadith, in principle, can not be accepted, because the right to determine the reliability and unreliability of the hadith have only Muhadith who have reached the degree of "al-Hafiz".

Imam al-Suyut in his book "Alpha" in the terminology of hadith says:

"Take it if it Hafiz said

Or from the collection, containing only reliable".

Also as an argument, you can hear that these hadiths are not given by Bukhari and Muslim, and therefore unreliable. This is an amazing word, because no Bukhari, no Muslim is not set for themselves the task to collect ALL the authentic hadith, as they clearly say in the preface to their collection. And so the fact of the absence of some of the hadith in Bukhari or Muslim does not automatically indicates its unreliability.

As for the meaning of the hadith, then, of course, not only a group of unbelievers will be in Hell, but also sinful Muslims, Ahlu-kabair (who committed major sins).

But fundamentally, we say that Ahlu-bida, the people who distort the religion, not unbelievers until they deny that definitely known from religion. For example, the fact that Allah is the Only Creator of the world, that He's perfect, He does not have inherent weaknesses, that the Prophet Muhammad, may Allah bless him and Muhammad is the last Prophet, there will be no other prophets and revelations, that prayer or fasting is obligatory, zina (adultery) or alcohol are prohibited and etc. If they deny it, as those who say that their teacher Ghulam Ahmad was a prophet, nabi (they say that he is not Rasul, he had no new Shariah or new books, but he got vahyu revelation from Allah), such people are believer.